Landau quantization and the thickness limit of topological insulator thin films of Sb2Te3

We report the experimental observation of Landau quantization of molecular beam epitaxy grown

Sb2Te3 thin films by a low-temperature scanning tunneling microscope. Different from all the reported

systems, the Landau quantization in a Sb2Te3 topological insulator is not sensitive to the intrinsic

substitutional defects in the films. As a result, a nearly perfect linear energy dispersion of surface states as

a 2D massless Dirac fermion system is achieved. We demonstrate that four quintuple layers are the

thickness limit for a Sb2Te3 thin film being a 3D topological insulator. The mechanism of the Landaulevel

broadening is discussed in terms of enhanced quasiparticle lifetime.